The invention relates to a system and method for protecting a receiver from jamming interference that may be present in a wireless communications system.
Wireless communication systems include digital communication systems, such as code-division multiple-access (CDMA), time-division multiple-access (TDMA) and Global System for Mobile Communications (GSM), and analog communication systems, such as the Advanced Mobile Phone Service (AMPS). Communications systems are often designed assuming the absence of malicious transmissions, jamming transmissions, or other electromagnetic interference that could disrupt normal communication traffic carried by the communications system.
A jamming signal transmission typically features a sufficiently strong signal strength to saturate radio frequency circuitry of a receiver. A jamming signal may include either a transient signal transmission (e.g., pulse) or a continuous transmission. A microwave signal blast within a receive bandwidth of the receiver is an example of a jamming signal. Such a microwave signal blast can temporarily disable the base station receiving function and crash an entire cell site that is otherwise operating reliably. If the jamming signal is sufficiently strong at different cell sites, communications at multiple cell sites may be disrupted.
In a CDMA system, power control of mobile stations is crucial to overall proper operation. More specifically, the transmit power levels of the mobile stations are controlled such that the interference between mobile stations is minimized and, in turn, system capacity is maximized. For effective power control in a CDMA system, jamming signals and interference from sources external to the communications system are assumed to be within tolerable limits. However, if the jamming signals or interference exceeds tolerable limits (e.g., as with ultra-strong jamming signals) the communications system, or a portion thereof, may fall into a temporary failure mode. During the temporary failure mode, calls may be dropped, access to the communications system may be denied, or communications may be disrupted.
One conventional interference reduction technique focuses on maximizing user capacity by rejecting undesired jamming signals through base-band signal processing within a receiver. However, the conventional interference reduction scheme may be ineffective because the received signal-to-noise ratio may be severely degraded in the receiver if a jamming signal with an ultra strong signal level disables normal operation of the radio frequency receiver. Thus, a need exists for an interference protection scheme that can reduce or eliminate the deleterious effects of ultra-strong jamming signals as well as jamming signals of lesser amplitude on receivers.
In accordance with the invention, an interference protection system is used with an antenna system to reduce the interference effects of a jamming signal. The antenna system is arranged to receive a desired signal, and is capable of producing a radiation pattern having a changeable null direction that may be directed toward an angle of arrival of a jamming signal to spatially filter out the jamming signal.
The present invention relates to an apparatus and method of using the antenna system for spatially filtering out the jamming signal. One aspect of the invention includes a detector and a controller that cooperate with the antenna system. The detector is capable of detecting a jamming signal received by the antenna system and distinguishing the jamming signal from the desired signal. The detector is adapted to produce a nonlinear signal (or another suitable signal) indicative of a received magnitude of the jamming signal. The controller is configured to control the antenna system based upon the nonlinear signal (or another suitable signal) produced by the detector. The controller controls the antenna system to spatially filter out the jamming signal from the desired signal by orienting the changeable null direction toward an angle of arrival of the jamming signal relative to the antenna system. The controller is adapted to vary the changeable null direction until the nonlinear signal is minimized, or otherwise reduced to an acceptable level, to spatially filter out the jamming signal from the desired signal.
The interference protection system can prevent the introduction of a jamming signal into a receiver, once the antenna system nulls the jamming signal in a transparent manner to users of the communications system. The interference protection system is well-suited for guarding against communication failures caused by ultra-strong jamming signals (e.g., a jamming signal exceeding xe2x88x9220 dBm at the antenna system), and jamming signals of lesser magnitude, because the receiver protection system allows a receiver to operate normally with minimal or no exposure to the jamming signal.